CHAPTEE VIII 



NEMATODA 



Chabactbeistics. — Animals with an elongated unsegmented body, 

 tapering at each end. A well-developed cuticle is secreted hy 

 the epidermis. A digestive system is present, and the eoscretory 

 system takes the form, of lateral ducts which open anteriorly 

 hy a median ventral pore. As a rule, they are dioecious, 

 and many are endoparasitic ; among the parasitic forms an 

 alternation of hermaphrodite and bisexual generations may 

 occur. A ciliated epithelium is universally absent. 

 The JTematoda are colloquially known as thread-worms. 

 The order contains a great number of species, many of them 

 parasitic ; in fact, there are said to be as many species of para- 

 sitic Nematodes as all the other endoparasites together. 

 About twenty different species attack man, and they occur in 

 almost every organ of the body, often inducing sufficient trouble 

 to cause death. The free species are usually small, often 

 microscopic. The parasitic forms are as a rule larger, the Guinea 

 worm, Filaria medinensis, which lives in the subcutaneous 

 tissues of men and horses in the tropics, attains a length of 

 6 feet, and the female Eustrongylus gigas, which lives in the 

 kidneys of mammals, may be 3 feet or more long. 



Ascaris lumbricoides inhabits the human intestine and 

 stomach, and is not uncommon in children. It is a white 

 cylindrical animal pointed at each end. The female measures 

 from 9 to 14 inches in length. The male is about half as 

 long ; it is rarer than the female, and may be distinguished by 

 its curved hinder end, and the presence of two bristles in the 

 neighbourhood of the anus. 



The mouth is terminal and surrounded by three lips, a 



